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Combating Early Bolting (Flowering) in Onions: An Indigenous Practice

An onion is classified as a biennial plant, which means it has a two-year lifespan. In ideal growing conditions, it would grow during the first year and then flower and produce seeds during the second year. However, if the plant experiences stress, it may enter a state of bolting, where it rapidly attempts to reproduce by flowering and producing seeds before it has fully matured. Bolting onions can be easily identified by their tall, solid stem and the appearance of a flower pod at the top, which eventually produces a round flower that results in the formation of seeds after pollination. Unfortunately, once an onion plant has seeded, it will stop growing, resulting in

small bulbs that do not store well. This is a problem for growers. In this chapter we shall discuss about how mechanical stress acts different from other kinds of stress and how it can be useful against onion bolting.

Mechanical Stress

Sessile organisms, like plants, are vulnerable to mechanical stresses from external forces such

as wind or water movements, which can regularly disturb ecosystems. When these forces exceed a plant's capacity to resist breakage, buckling, or uprooting, mechanical failure occurs. To adapt to adverse environmental conditions, different plant strategies have been defined, varying according to the factor considered and the level of study. Plant resistance, which minimizes the negative impact of adverse conditions, can be achieved through avoidance or tolerance. Avoidance involves traits that prevent deleterious effects, while tolerance enables plants to endure adverse conditions. In the case of mechanical forces, plant resistance relies on either avoidance or tolerance strategies. In this particular case of onion, we theorize the use of mechanical stress to combat bolting (Flowering) in onions. It is evidential (New Phytologist , 2011) that if plants are under mechanical stress, they allocate resource in to combating such stress which may result in lack of resources for Fitness Enhancing Functions like Flowering and Seeding.

Deliberate Mechanical Stress (Pinching and pressing)

Deliberate mechanical stress is a practice that we found among the local people of Madi and surrounding region used particularly among the onions to stop them from early bolting. After the onion has reached a healthy age (with its well developed root and shoot) the bottom shoot is pinched and pressed with thumb resulting the plant to lay down horizontally on the bed. Once all the pinching and pressing is done, it is left to recover for some days.

In picture: Close shot of pinching and pressing onion stem

The plants under healthy conditions recover in a few days again standing upright vertically. After the plants have recovered, in around a 7-10 days time, the worker observes the plant and undertakes the same deliberate mechanical stress procedure.

In picure: Onion plant receiving mechanical stress through pinching and twisting

The onion bulbs are observed regularly and stress is provided while also ensuring that enough time has been given to help it recover completely as too much stress and lack of recovery period can be detrimental to the plant.

In picture: Onion plants recovering after the earlier mechanical stress

This blog on onion is to be continued. We shall update the progress of the bulbs after harvest.

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